1. Field of the Invention
The present invention relates to a milling machine which produces crushed stones by crushing an arbitrary ore through use of predetermined crushing members stored in a shell main unit, to a method of crushing an ore through use of the milling machine, and to a method of manufacturing the milling machine.
2. Description of the Related Art
In principle, a shell main unit of a conventional milling machine is formed into the shape of a hollow cylinder. A milling machine has a shell main unit of one of the below-described types intended for improving the efficiency of crushing ore by dropping and rotating grinding members provided in the shell main unit. For example, when the shell main unit is viewed from the side, an ore-feeder portion of the shell main unit is formed into the shape of a hollow cylinder, whereas an outlet portion of the shell main unit is formed into the shape of a hollow truncated cone tapered toward the direction of discharge. Another type of shell main unit has a reverse structure; namely, the ore-feeder portion of the shell main unit is formed into the shape of hollow truncated cone, whilst the outlet portion of the same is formed into the shape of a hollow cylinder. The grinding member is formed into the shape of a sphere or a deformed rectangular polyhedron.
The efficiency of crushing ore has been known to be improved by uniform and balanced distribution of grinding members within the shell main unit. The reason for this is that uniform distribution of grinding members results in crushing action uniformly acting on ore, thereby enabling excessive crushing of ore and energy loss. Since the amount of crushing energy to be dissipated is proportional to the size of a substance to be crushed, crushing action is uniformly exerted on ore by uniform distribution of crushing members, thereby improving the quality of crushed stones.
However, in the milling machine which has conventionally been utilized, the shape of the milling machine makes attainment of uniform distribution of crushing members within the shell main unit difficult. For this reason, the conventional milling machine experiences difficulty in greatly improving the efficiency of crushing ore and is apt to cause excessive crushing of ore.